Traditionally, Code Division Multiple Access (CDMA) systems such as Interim Standard-95 (IS-95) and Wideband Code Division Multiple Access (WCDMA) are designed to handle many low or medium bit rate users, creating a rather smooth and relatively slow changing interference. However, the current trend goes towards much more bursty traffic with high rate demands. Examples of application resulting in such behavior include for example World Wide Web (WWW) applications and peer-to-peer traffic. Such applications will generate highly varying data rates compared to speech and video services typically are associated with rather constant and moderate bit rates.
In WCDMA users are non-orthogonal to each other in the up link (UL) thereby generating interference between each other even within the same cell. Therefore the system has an upper interference limitation, where the cell noise can not be increased further if the system shall remain stable. This limits the maximum cell capacity.
One way to handle both the more bursty traffic and the lack of orthogonality is to use Time-division between the users instead of codes, and thereby increase the UL WCDMA efficiency, see FIG. 1. In FIG. 1 the principle difference between normal code multiplexed scheduling and time division scheduling is schematically depicted for three users. As is apparent the use of a time division scheduling increases the possibility to transmit high data rates.
Time Division Multiple Access (TDMA) is a well-known method for divide the resources in cellular system.
The basis of a TDM scheme for WCDMA Enhanced Uplink (EUL) with a 2 ms Transmission Time Interval (TTI), is depicted in FIG. 2a. The TDM users are typically scheduled per Hybrid Automatic Repeat Request (HARQ) process. In EUL there are 8 HARQ processes for a 2 ms TTI. As a result, if one user is scheduled for HARQ process x, it typically is x+8 TTIs until the next transmission. To use the same HARQ process number is efficient since if user has to retransmit, it can automatically use the previous HARQ process number for the retransmission, without having to perform any scheduling. It should also be noted that TDM users can also use two (or more) continuous HARQ processes, as shown in FIG. 2b. 
When CDM is used, All HARQ process in accordance with 3GPP specification TS 25.321 is activated for the UE, i.e. as long as the UE has a grant greater than zero, it can use any HARQ process to transmit the data, until a grant zero (i.e. not allowed to transmit any data) is received. For the 2 ms TTI it is also possible to use the “Per HARQ process”, see 3GPP specification TS 25.321, chapter 9.2.5.2.2. This can be used to achieve time division between users. Node-B schedule allocates only one user for each HARQ process, i.e. Node-B transmits an absolute grant to the UE which is valid for a specific HARQ process until a new grant is received. The valid HARQ process is decided by the CURRENT_HARQ_PROCESS_ID, see section 11.8.1.4 in 3GPP Specification TS 25.321.
Further, in FIG. 3 a rough estimate of the cell capacity for different number of users per cell using theoretical calculations is shown. In FIG. 3 it is assumed that the users transmit simultaneously, so that full buffers are assumed. FIG. 3 shows the big difference in terms of capacity between one user transmitting such as in a Time Division Multiplexing scheme and one or more users transmitting such as in a Code Division Multiplexing (CDM) scheme. As can be seen in FIG. 3, the lack of orthogonality between users in the same cell quickly decreases the possible cell capacity. A cell with TDM scheduling will be able to maintain the high cell throughput for more than one user. The TDM capacity will also decrease with the number of users, due to more control signaling and less efficient TDM scheduling, but much more slowly than for a CDM system. The aim with TDM is to even with quite many high data rate user be able to maintain the cell capacity.
A problem arising when using TDM scheduling for a EUL WCDMA system, is that the 3GPP specification makes it difficult to handle too many TDM users efficiently. Thus, when many TDM users use the up-link simultaneously there will be an unacceptably long time between the transmission attempts for each user. A long time between the transmission attempts for each user will negatively impact the user experiences because it:                gives bad throughput for TDM users—not able to reach high bit rates,        has a long ping time for first packet, and        is not acceptable for any time critical data.        
Another problem is related to the fact that some TDM users are not utilizing the bandwidth available in a TDM scheme. Examples of such applications are Voice over IP (VoIP) and chat applications such as chat clients, email, presence etc. In FIG. 4, the problem is illustrated. As can been seen in FIG. 4 the user 2 is not fully utilizing the bandwidth provided in the TDM scheme.
There is a constant desire to improve the utilization bandwidth in radio communication. Hence there exists a need to improve the use of bandwidth in a cellular radio system, in particular a WCDMA radio system.